Anterior Cruciate Ligament Reconstruction with Femoral Direct Fiber Insertion: A Novel Technique

Anterior cruciate ligament (ACL) tears are among the most common injuries treated in sports medicine. The ACL plays a critical role in maintaining the static and dynamic stability of the knee joint, and its injury often leads to significant functional impairment. Accurate positioning of the femoral and tibial tunnels during ACL reconstruction is essential for restoring knee stability and kinematics. Traditional techniques, including single-bundle and double-bundle reconstructions, have been widely used, but they often fail to fully restore the knee’s biomechanical properties. This paper introduces a novel surgical technique for ACL reconstruction that focuses on the direct fiber insertion of the ACL at the femoral attachment site, aiming to improve functional outcomes.

Background and Rationale

The ACL is composed of two functional bundles: the anteromedial (AM) bundle and the posterolateral (PL) bundle. These bundles work synergistically to stabilize the knee during various movements. The femoral insertion of the ACL consists of direct and indirect fibers. Direct fibers attach closer to the resident ridge in a ribbon-like shape, while indirect fibers are more dispersed. Studies have shown that the direct fibers contribute significantly to the knee’s resistance to anterior tibial displacement, accounting for 66% to 84% of the resistance in the tibial anterior drawer test. In contrast, indirect fibers contribute only 11% to 15%. Finite element analysis further confirms that the stress on the ACL is predominantly concentrated in the direct fiber insertion area.

Traditional ACL reconstruction techniques, whether single-bundle or double-bundle, often place the femoral tunnel in the center of the ACL footprint, which is more inclined toward the indirect fibers. This may explain why these techniques do not consistently restore the knee’s stability and kinematics. The novel technique described in this paper focuses on reconstructing the ACL at the direct fiber insertion site, which is believed to be more effective in restoring knee function.

Surgical Technique

The surgical procedure begins with arthroscopic confirmation of the ACL tear. A hamstring tendon autograft is harvested and prepared for the reconstruction. The graft is divided into two or three strands, with the larger diameter strand used for the AM bundle and the smaller one for the PL bundle. The resident ridge and bifurcated ridge are exposed using a shaver and an electrothermal device, while the posterior indirect fibers and synovium of the ACL femoral insertion are preserved. The ACL stump at the tibial insertion is also preserved as much as possible.

The key step in this procedure is locating the direct fiber insertion. The intersection of the posterior femoral cortex and the Blumensaat line is identified, and the direct fiber insertion point is located on the extension line of the posterior femoral cortex on the medial side of the lateral femoral condyle. The AM bundle bone tunnel is positioned as far back as possible, with the posterior wall of the tunnel 1 to 2 mm thick and the bone bridge between the AM and PL tunnels 1 to 2 mm wide. The knee is flexed to 120° during drilling to ensure that the tunnels are more horizontal and to preserve the integrity of the posterior wall of the femoral anteromedial tunnel.

The tibial tunnel is drilled using a tibial drill guide system with a 5 to 8 mm diameter reamer. Bone files are used to smooth the intra-articular tunnel outlets of the tibia and femur tunnels to minimize sharp edges. The PL graft is first transplanted into the PL tunnel, followed by the AM graft. The femoral end is fixed with an adjustable extra-cortical suspended titanium plate, and the tibial end is fixed with an absorbable interference screw at the knee’s extension position.

Postoperative Rehabilitation

Postoperatively, patients wear a long leg brace for two months. Partial or full weight-bearing activities are allowed, and patients can walk with crutches. Active flexion and passive extension of the knee are encouraged starting on the second day after surgery. Jogging is permitted after three months, non-confrontational activities after six to nine months, and gradual return to confrontational sports after twelve months.

Clinical Evaluation

The effectiveness of the procedure is evaluated using several clinical tests and scoring systems, including the Pivot shift test, Lachman test, Lysholm score, International Knee Documentation Committee (IKDC) score, and KT-2000 side-to-side difference. Three-dimensional computed tomography (3D-CT) is performed during the first week after surgery to confirm the position of the bone tunnels in the direct fiber insertion area. Three-Tesla magnetic resonance imaging (MRI) is used to assess graft healing and shaping two years postoperatively.

Between June 2016 and June 2018, 26 patients (15 males and 11 females) with an average age of 30.5 years underwent this novel procedure. The average time between injury and surgery was 7.3 days. No graft ruptures, fractures, tunnel fusions, or impingements occurred during the operation. The average surgery time was 56.16 minutes, and the average intraoperative bleeding volume was 35.31 mL. No infections were reported.

Preoperatively, the Pivot shift test results were grade I in two cases, grade II in eleven cases, and grade III in thirteen cases. The Lachman test results were grade II in eight cases and grade III in eighteen cases. Postoperatively, all cases were negative for the Pivot shift test, and only one case had a grade I Lachman test result. Two years after surgery, all patients had negative Pivot shift and Lachman test results, indicating restored anterior and rotational stability of the knee.

The Lysholm score improved from a preoperative value of 56.50 to 88.50 at two years postoperatively, and the IKDC score increased from 48.30 to 92.50. The KT-2000 side-to-side difference decreased from 5.60 mm preoperatively to 1.50 mm at two years postoperatively. MRI examinations two years after surgery showed uniform low signal intensity in the ACL grafts on T2-weighted images, with no significant enlargement of the bone tunnels. The grafts were well-shaped and mature, with no impingement observed between the grafts and the intercondylar fossa.

Biomechanical Analysis

Finite element analysis revealed that the maximum stress regions of the patella and femoral trochlea in the affected knee were similar to those in the contralateral knee, with no significant difference in stress values. This suggests that the novel surgical procedure effectively restores the mechanical function of the knee.

Discussion

The most significant feature of this novel technique is the placement of the femoral tunnel in the center of the direct fiber insertion rather than the center of the ACL footprint. This approach provides more isometric effectiveness during full knee flexion, which is not achieved with traditional ACL reconstruction techniques. Biomechanical studies have shown that double-bundle ACL reconstruction with smaller graft diameters can better cover the footprint and restore knee kinematics and rotational stability compared to single-bundle techniques with larger diameters.

The identification of the direct fiber insertion under arthroscopy is crucial for the success of this procedure. Cadaveric studies and 3D-CT imaging were used to determine the accurate position of the femoral tunnel before this technique was applied clinically. Microscopic and histological observations have shown that the direct fiber insertion is located approximately 4 mm from the posterior cartilage edge of the femoral condyle, providing a reference for tunnel preparation.

Limitations

This study has some limitations. First, the clinical effectiveness of this procedure needs to be confirmed with a larger sample size. Second, second-look arthroscopy was not performed, so the tension, retear, and synovialization of the grafts could not be assessed. Finally, long-term clinical studies are necessary to evaluate the durability of this technique.

Conclusion

ACL reconstruction with femoral direct fiber insertion is a novel and effective surgical technique that restores the anterior stability of the tibia and the rotational stability of the knee. It provides excellent early-stage clinical outcomes and effectively restores the knee’s kinematic environment. This technique represents a significant advancement in ACL reconstruction, offering improved functional outcomes compared to traditional methods.

doi.org/10.1097/CM9.0000000000001771

Was this helpful?

YesNo

0 / 0